Warm the olive oil in a large pot or Dutch oven over medium heat then toss in the onion and the fennel. Cook for 2-3 minutes.
Next add the carrots, garlic, and sweet potato along with the spices. Stir together and cook for 1 minute then pour in 1/2 cup vegetable broth. Bring to a low boil and cook for 15 minutes so that the liquid reduces by approximately 1/3.
Pour in the remaining broth along with the rinsed lentils and bring to a boil. Reduce to a simmer and cook for 20 minutes, or until the lentils are tender.
Turn off the heat and then squeeze in the lemon juice and stir together. Ladle into individual bowls for serving and top with cilantro and radishes (optional). Serve warm and enjoy!